O.K. Giving you a recent example to show that sitting on your profit is not enough... Today's market may make you flat or place you underground even when you were sitting on profit.
29th March, 2012 was an expiry when market closed below 5200 (5180 NF to be precise). Good amount of short positions were in the system as market closed below 5200 psychological level at expiry. The very next day market gaped up 55-60 points. The bears were trapped and the market continued moving up... Nifty futures comfortably traded above 5300 and never came down on that day below 5300 once crossed (remember Casper... you told that market is afraid of crossing 5300 and will not... somebody replied that if it has tried so many times & it will)... so day traders who have taken position at opening of the market should have comfortably waited to book profit at day's end (adds on initial position would be malai maarke :lol
...
Alas! it was not to be... MNF traded below the
LOWER LIMIT (yes, you read it right... It was around 47-4800... ) on that day for few sec... so some unfortunate people keeping s/l-m @ 5300 just lost their profitable positions as well as booked a good chunk of loss due to vagaries of the market as well as the foolish decision-making of keeping s/l-m... Questions were raised... Zerodha and Sumo said it's part & parcel of trading... Later on Zerodha clarified that NSE reversed the trade happened at the lowest price (yeah... the authority cleared the sh**
Even EOD charts do not have those price points)... BTW, MNF closed at 5322 on that day...
The above-mentioned 2 examples gave me enough insights to avoid keeping S/L-M orders in the system and giving the market signed blank cheque to rob me at will...